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1. also re·press·er One that represses.
2. Genetics A protein that binds to an operator, blocking transcription of an operon and the enzymes for which the operon codes.
(Genetics) biochem a protein synthesized under the control of a repressor gene, which has the capacity to bind to the operator gene and thereby shut off the expression of the structural genes of an operon
a protein that binds DNA at an operator site and thereby prevents transcription of one or more adjacent genes.